The present invention is generally related to processing semiconductor wafers, and more particularly to a method and apparatus for breaking a processed wafer into individual die and transferring the wafer to a wafer carrier for pick and place equipment that packages the die.
In the manufacture of semiconductor devices, it is conventional to form many integrated circuits or devices upon a single wafer of semiconductor material, such as silicon. After the devices have been formed on the wafer, it is necessary to separate each device from one another such as by completely cutting the wafer into segments on which one or more devices or circuits have been formed, these segments commonly being referred to as die. For devices that are unsuitable for a complete saw process due to handling constraints, such as micromechanical devices including the Digital Micromirror Device (DMD) manufactured by Texas Instruments of Dallas, Tex., the separation of the individual die may also be undertaken by a wafer break process. Orthogonal lines may be scribed on the wafer, or a partial saw can be performed on the wafer streets extending between devices, the saw lines commonly being known as kerfs. The wafer is then broken along these wafer kerfs to form individual die. If care is not taken during the breaking of the wafer, the individual die may be partially fractured or broken.
During the wafer break process, the fabricated wafer may be placed upon a stretchable membrane such as a wafer tape having an adhesive on one side. As the wafer is broken, the tape is stretched to further separate the formed die from one another to avoid the die corners from rubbing against one another. After the wafer break process, pick and place equipment removes the individual die from the tape. These die are then packaged with leads and pins, the packaging comprising plastic, ceramic or other suitable material. Sometimes, the die are hermetically sealed in the package to prevent moisture from damaging the device, particularly if the device is a micromechanical device having moving parts.
The breaking of the wafer into die can be performed using any of several conventional methods. In one process, a roller is rolled across the back side of the inverted partially sawn semiconductor wafer. Using another method, the wafer can be supported upon an adhesive saw tape, inverted, and flexed outwardly with a hemispherical dome. Such techniques are shown in commonly assigned U.S. Pat. No. 3,562,057 to McAlister, et al, and also in U.S. Pat. No. 5,104,023 to Nishiguchi, et al. In these two patents, the semiconductor wafer is supported upon a flexible tape membrane, inverted, and pressed downwardly by a spherical dome.
In the commonly assigned patent application Ser. No. 08/367,970 entitled xe2x80x9cMethod and Apparatus for Breaking and Separating Dies from A Waferxe2x80x9d, and also in commonly assigned patent application Ser. No. 08/485,168, entitled xe2x80x9cMethod and Apparatus for Breaking and Separating Dies from A Waferxe2x80x9d, there is disclosed a method and apparatus for separating a wafer and the handling of the wafer tape after the break process.
It is desired to provide an improved method and apparatus for breaking a semiconductor wafer into die, and a method for expanding the saw film during and after the wafer break process. It is especially desired to provide an improved and simpler method for breaking and handling wafers comprised of micromechanical circuits, such as the DMD, to minimize the generation of particles and prevent the mechanical rubbing of die after the break process. It is further desired to provide an improved method and apparatus for transferring the wafer tape and die to a wafer carrier which is suited for automated pick and place die removing equipment which facilitates the die packaging process.
The present achieves technical advantages as a method and apparatus including a large flex-frame supporting a wafer saw film tape and wafer during the wafer saw and break process, whereby a transfer cylinder encompasses a break dome to stretch the saw film as it pushes the wafer film off the breaking dome and transfers the wafer film to a smaller second frame. This second smaller frame receives the sticky surface of the wafer tape, and is juxtaposed with the sliding transfer cylinder. The rim of the transfer cylinder encompassing the break dome forces the sticky surface of the saw film into contact with the smaller second flex-frame with sufficient pressure to cause the tape to sufficiently adhere to the smaller flex frame. A resistance heating wire is positioned around the outer periphery of the transfer cylinder rim. This wire is heated, causing the saw film to melt such that the saw film easily separates from the large flex-frame following transfer. The small second flex-frame holding the saw film and broken wafer is then transferred to a carrier, this carrier being suited to automated processing equipment which ultimately packages the die. A support base supports the large flex-frame and has upwardly extending walls defining a cavity, with the smaller second flex-frame residing within this cavity. The transfer cylinder pushes the stretched saw film tape and broken wafer downwardly into the cavity until the stretched saw film tape is supported by the smaller flex-frame.